Process for producing organic acids

ABSTRACT

An improvement in a process for converting an unsaturated, acyclic hydrocarbon to an acid in which the unsaturated, acyclic hydrocarbon is reacted with oxygen containing a small amount of ozone at a low temperature to obtain an intermediate product in a first stage and the intermediate product is oxidized in a second stage with molecular oxygen at a higher temperature to obtain the desired carboxylic acid, which involves heating the intermediate product in the absence of additional oxygen prior to the second stage oxidation, whereby explosive hazards in the second stage are minimized.

United States Patent Ellis et al.

[72] Inventorsi Alan F. Ellis, Murrysville; Alfred N. Kresge, Verona;Richard Seekircher, Cheswick, all of Pa.

[73] Assignee: Gulf Research & Development Company, Pittsburgh, Pa.

[22] Filed: Nov. 28, 1969 [21] Appl. No.: 880,890

[52] US. Cl. ..260/533 R, 260/413 [5 l Int. Cl ..C07c 51/32 [58] FieldoiSearch ..260/533 R, 533 C,4l3

[56] References Cited UNITED STATES PATENTS 3,557,166 l/l97l Lachowicz..260/533 R 3,219,675 11/1965 Seekircher ..260/533 C 3,238,250 3/1966Bailey ..260/533 R 3,441,604 4/1969 Baylis et al. ..260/533 C PROCESSFOR PRODUCING ORGANIC ACIDS 51 July 11,1972

OTHER PUBLICATIONS Noller Chemistry of Organic Compounds, 3rd ed.Saunders (l965)pg. 101.

Primary ExaminerLorraine A. Weinberger Assistant ExaminerRichard D.Kelly Attorney-Meyer Neishloss, Deane E. Keith and Joseph J. Carducci [57] ABSTRACT An improvement in a process for converting an unsaturated,acyclic hydrocarbon to an acid in which the unsaturated, acyclichydrocarbon is reacted with oxygen containing a small amount of ozone ata low temperature to obtain an intermediate product in a first stage andthe intermediate product is oxidized in a second stage with molecularoxygen at a higher temperature to obtain the desired carboxylic acid,which involves heating the intermediate product in the absence ofadditional oxygen prior to the second stage oxidation, whereby explosivehazards in the second stage are minimized.

9 Claims, No Drawings PROCESS FOR PRODUCING ORGANIC ACIDS This inventionrelates to a process for converting an unsaturated, acyclic hydrocarbonto an organic carboxylic acid by using ozone and oxygen while minimizingexplosive hazards associated therewith. More specifically, thisinvention relates to an improvement in the process wherein anunsaturated, acyclic hydrocarbon is subjected to ozonolysis in a firststage and the product resulting therefrom is subjected to oxidation in asecond stage with molecular oxygen to obtain organic carboxylic acidscorresponding to said unsaturated, acyclic hydrocarbon.

Unsaturated, acyclic hydrocarbons which can be used herein can bestraight or branched chain olefins, terminal as well as internal, havingfrom four to 40 carbon atoms, preferably from six to 30 carbon atoms.Specific examples of olefins that can be used are butene-l, octene-l,undecene-l, eicosene-l octene-2,dodecene-3, tetradecene-7 nonadecene-8,3-methylpentene-l, 4-ethyldecene-2, 3- methyl-4-ethyl-nonene-l etc.

The ozonolysis procedure used in the first step can follow anyconventional outline. Thus, for example, a stream of gas containingmolecular oxygen, such as oxygen itself, and from about 0.5 to about 6,or even higher, but preferably about 2 to about 3 percent, by weight ofozone relative to oxygen is passed continuously through the olefincharge dissolved in a suitable solvent, for example, a carboxylic acidhaving from two to ten carbon atoms, such as acetic acid, propionicacid, heptanoic acid and decanoic acid, or an alcohol having from one tosix carbon atoms, such as methanol, propanol-I, hexanol-l etc., at sucha rate so that the exit stream will be substantially free of ozone,continuing until some ozone is found in the exit gas, at which time theozonolysis reaction will have terminated. Since ozonolysis issubstantially instantaneous, the time of contact depends upon obtainingsuitable contact between ozone and unreacted olefin. The temperature canbe from about 20 to about 35 C., preferably about to about C., and whilepressures as high as about 50 pounds per square inch gauge can beemployed, atmospheric pressure is preferred. As a result of ozonolysis,cleavage of the olefinic double bond occurs and the individual fragmentsso produced react with ozone and are believed to form aldehydes andhydroperoxides. Thus, the olefin for example, R and R" being alkylsubstituents, is believed to be converted to wherein R' represents analkyl group, in the case of an alcohol solvent, and an acyl group, inthe case of an acid solvent. The hydroperoxide is believed to resultfrom the addition reaction of the intermediate Zwitterion with thesolvent therein.

The aldehydes and hydroperoxides so produced are then subjected tooxidation in a second stage with a gas containing molecular oxygen,preferably air. Any effective method which insures contact between thealdehyde and the hydroperoxide and oxygen can be used. In a preferredembodiment air is continuously passed through the ozonolysis product andthis is preferably continued until there is no noticeable reduction inoxygen content of the exit stream. The amount of oxygenstoichiometrically needed, relative to the ozonolysis product, definedas consisting essentially of aldehydes and hydroperoxides, on a molarbasis must be at least about 1:1, but in general from about 5:1 to about100:], is used. Temperatures ofabout 70 to about 150 C., preferablyabout 80 to about I 10 C., can be used. Pressures as high as about 100pounds per square inch gauge can be employed, but in general atmosphericpressure is preferred. A reaction time of about 0.5 to about 2 hourswill generally suffice. As a result of the oxidation step it is believedthe aldehydes are oxidized and the hydroperoxides are rearranged to thecorresponding organic carboxylic acids. Recovery of the organiccarboxylic acids from the reaction mixture can be effected in anydesired manner, but in general fractional distillation is preferred.

Unfortunately, we have found in our studies that during the oxidation inthe second stage the vapor phase above the ozonolysis product throughwhich molecular oxygen is being passed has potentially an explosivelyviolent nature. We believe this occurs because the passage of molecularoxygen through the ozonolysis product removes therefrom some of thehydroperoxide therein and the latter forms a mixture with unreactedmolecular oxygen that has passed therethrough and it is this mixturethat can explode.

We have found that the hydroperoxide content of the ozonolysis productcharged to the second stage can be substantially reduced, therebyminimizing the amount thereof that can find its way into the vapor spaceabove the product being treated in the second stage and reducing theexplosive character thereof, by heating the ozonolysis product obtainedin the first stage in the absence of added oxygen prior to oxidation inthe second stage. We believe that such heating converts thehydroperoxide to the corresponding aldehydes and acids. The latter arethe desired acids and the aldehydes so produced, together with thealdehydes obtained in the first stage, are then oxidized to thecorresponding acids in the second stage in the manner hereinabovedefined. Fortuitously,

the yield of desired acids is not adversely affected by the heatingstep.

In conducting the intermediate heating step the ozonolysis product fromthe first stage, consisting essentially of the defined aldehydes andhydroperoxides, is heated at a temperature of about to about 140 C.,preferably about l00 to about C., a pressure of about atmospheric toabout 200 pounds per square inch gauge, preferably about atmospheric toabout 50 pounds per square gauge, for about 1 minute to about 30minutes, preferably for about 10 minutes to about 20 minutes. As noted,no oxygen is added to the ozonolysis product during such intermediateheating, and any oxygen which may be present, which does not adverselyaffect the operation, is that small amount that may be present as aresult of entrainment in the first stage, that which may be in the airin the reaction zone or that which may be released in the decompositionof the hydroperoxide. It is critical that the above temperature and timelimitations be strictly observed. At lower temperatures, the reactiontime necessary for the decomposition of the hydroperoxides becomes toolong, whereby the formation of polymers and other by-products isfavored. At higher temperatures the decomposition reaction proceeds tooviolently, thus presenting a potentially hazardous situation in additionto a tendency for formation of undesired byproducts.

The process of this invention can further be illustrated by thefollowing.

EXAMPLE I 20 grams of octene-l were dissolved in 80 grams of propionicacid and the resulting mixture was cooled to a temperature of 4 C. Anoxygen stream containing from three to 4 percent by weight of ozone waspassed through the mixture over a period of about 3 hours at a rate ofabout I liter per minute while maintaining the temperature of thereaction mixture at 5 to 8 C. The reaction product was found to have aperoxide number of 2180. By peroxide number we mean milliequivalentactive oxygen per 1,000 grams of product when determined by aniodometric method. By active oxygen" we mean the oxygen in theozonolysis product associated with the hydroxyl group forming thehydroperoxide. The reaction product was then maintained at a temperatureof 100 to 108 C. for 60 minutes while air was passed therethrough at arate of 1 liter per minute. The resulting product was subjected todistillation sufficient to remove propionic acid therefrom. It was foundthat 94.3 percent by weight of the remainder was heptanoic acid, withsubstantially the rest being hexanoic acid and neutral compounds.

EXAMPLE 11 The run of EXAMPLE 1 was repeated except that the ozonolysisproduct at the end of the first stage was heated at a temperature of 100to 109 C. and atmospheric pressure, in the absence of additional oxygen,over a period of minutes, prior to treatment in the second stage. Theperoxide number of the heated mixture was 355. The final product wasfound to contain 94.3 percent by weight of heptanoic acid, with theremainder being substantially hexanoic acid and neutral compounds.

EXAMPLE Ill grams of tetradecene-7 were dissolved in 80 grams ofpropionic acid and the resulting mixture was cooled to a temperature of4 C. An oxygen containing from three to 4 percent by weight of ozone waspassed through the mixture over a period of 100 minutes at a rate ofabout 1 liter per minute while maintaining the temperature of thereaction mixture at 7 to 9 C. The reaction product was found to have aperoxide number of 2120. The reaction product was then maintained at atemperature of 100 to 108 C. for 60 minutes while air was passedtherethrough at a rate of 1 liter per minute. The resulting product wassubjected to distillation sufficient to remove propionic acid therefrom.lt was found that 92.2 percent of the remainder was heptanoic acid, withacids of lower and higher molecular weight and some neutral compounds asbyproducts.

EXAMPLE IV The run of EXAMPLE I" was repeated except that the ozonolysisproduct at the end of the first stage was heated at a temperature of 100to 108 C. and atmospheric pressure, in the absence of additional oxygen,over a period of 15 minutes, prior to treatment in the second stage. Theperoxide number of the heated mixture was 575. The final product wasfound to contain 91.9 percent by weight of heptanoic acid. Thebyproducts consisted of acids of lower and higher molecular weight andsome neutral compounds.

A comparison of the runs in which an intermediate thermal treatmentwithout oxygen was applied with those in which the oxidation stepfollowed the o'zonization step immediately shows that the thermaltreatment reduces the peroxide content of the mixture to a level whichcan be considered essentially safe in terms of formation of an explosivemixture in the vapor phase.

Obviously, many modifications and variations of the invention, ashereinabove set forth, can be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

We claim:

1. In a process for converting an unsaturated, acyclic hydrocarbonhaving from four to 40 carbon atoms to an acid wherein the unsaturated,acyclic hydrocarbon is reacted with ozone at a lower temperature ofabout 20 to about 35 C. to obtain an intermediate product in a firststage and the intermediate product is oxidized in a second stage withmolecular oxygen at a higher temperature of about 70 to about 150 C.

to obtain the desiredcarboxylic acid, the improvement which comprisesheating said intermediate product in the absence of added oxygen priorto said oxidation in said second stage at a temperature of about toabout 140 C.

2. The process of claim 1 wherein said heating of said inter mediateproduct prior to said second stage is in the temperature range of aboutto about C.

3. The process of claim 1 wherein said heating of said intermediateproduct prior to said second stage is within a period of about 1 toabout 30 minutes.

4. The process ofclaim 1 wherein said heating of said intermediateproduct prior to said second stage is within a period of about 10 toabout 20 minutes.

5. The process of claim 1 wherein the temperature in said first stage iswithin the range of about 10 to about 20 C.

6. The process of claim 1 wherein the temperature in said second stageis within the range of about 80 to about 1 10 C.

7. The process of claim 1 wherein said unsaturated, acyclic hydrocarbonhas from six to 30 carbon atoms.

8. The process of claim 1 wherein said unsaturated, acyclic hydrocarbonis octene-I.

9. The process of claim 1 wherein said unsaturated, acyclic hydrocarbonis tetradecene-7.

2. The process of claim 1 wherein said heating of said intermediateproduct prior to said second stage is in the temperature range of about100* to about 120* C.
 3. The process of claim 1 wherein said heating ofsaid intermediate product prior to said second stage is within a periodof about 1 to about 30 minutes.
 4. The process of claim 1 wherein saidheating of said intermediate product prior to said second stage iswithin a period of about 10 to about 20 minutes.
 5. The process of claim1 wherein the temperature in said first stage is within the range ofabout 10* to about 20* C.
 6. The process of claim 1 wherein thetemperature in said second stage is within the range of about 80* toabout 110* C.
 7. The process of claim 1 wherein said unsaturated,acyclic hydrocarbon has from six to 30 carbon atoms.
 8. The process ofclaim 1 wherein said unsaturated, acyclic hydrocarbon is octene-1. 9.The process of claim 1 wherein said unsaturated, acyclic hydrocarbon istetradecene-7.